Method and device for deriving block structure in video coding system

ABSTRACT

A video decoding method performed by a decoding device, according to the present invention, comprises the steps of: deriving at least one reference block for an object block; deriving a partitioned structure of the object block on the basis of a partitioned structure of the at least one reference block; partitioning the object block into a plurality of sub blocks on the basis of the derived partitioned structure; and generating recovered samples by decoding the plurality of sub blocks. According to the present invention, a partitioned structure of a current picture can be derived on the basis of a reference block of a neighboring picture, and thus the amount of data used in the additional information signaled for partitioning of the current picture can be reduced and overall coding efficiency can be improved.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage application under 35 U.S.C. § 371of International Application No. PCT/KR2016/002742, filed on Mar. 18,2016, the disclosure of which is herein incorporated by reference in itsentirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a video coding technique, and moreparticularly, to a coding method and apparatus based on efficient blockstructure derivation in a video coding system.

Related Art

Demand for high-resolution, high-quality images such as HD (HighDefinition) images and UHD (Ultra High Definition) images have beenincreasing in various fields. As the image data has high resolution andhigh quality, the amount of information or bits to be transmittedincreases relative to the legacy image data. Therefore, when image datais transmitted using a medium such as a conventional wired/wirelessbroadband line or image data is stored using an existing storage medium,the transmission cost and the storage cost thereof are increased.

Accordingly, there is a need for a highly efficient image compressiontechnique for effectively transmitting, storing, and reproducinginformation of high resolution and high quality images.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method andapparatus for improving video coding efficiency.

It is another object of the present invention to provide a method andapparatus for efficiently deriving a block structure in a picture.

It is further another object of the present invention to provide amethod and apparatus for deriving a block structure of a current picturebased on neighboring pictures.

It is further another object of the present invention to provide amethod and apparatus for dividing a current picture using divisioninformation of neighboring pictures.

It is further another object of the present invention to provide amethod and apparatus for dividing a current picture with small amount ofdata.

According to an embodiment of the present invention, there is provided avideo decoding method performed by a decoding apparatus, the methodincluding deriving at least one reference block for a target block,deriving a division structure of the target block based on a divisionstructure of the at least one reference block, dividing the target blockinto a plurality of blocks based on the derived division structure, anddecoding the plurality of blocks to thereby generate reconstructedsamples.

According to another embodiment of the present invention, there isprovided a video encoding method performed by an encoding apparatus, themethod including deriving at least one reference block for a targetblock, deriving a division structure of the target block based on adivision structure of the at least one reference block, dividing thetarget block into a plurality of blocks based on the derived dividedstructure, and encoding the plurality of detail blocks to thereby outputan encoding parameter.

According to the present invention, the division structure of thecurrent picture may be derived based on the reference block of theneighboring picture, through which the amount of data used for theadditional information signaled for the division of the current picturemay be reduced, and the overall coding efficiency may be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram schematically illustrating a video encodingdevice according to an embodiment of the present invention.

FIG. 2 is a block diagram schematically illustrating a video decodingdevice according to an embodiment of the present invention.

FIG. 3 illustrates an example of a fixed block division structure and avariable block division structure.

FIG. 4 illustrates the concept of coding unit division.

FIG. 5 illustrates an example of coding unit division.

FIG. 6 illustrates examples of forward division and non-forwarddivision.

FIG. 7 illustrates an example of information necessary for unit blockdivision.

FIG. 8 illustrates an example a reference block of a neighboring pictureand a subject block of a current picture corresponding to the referenceblock.

FIG. 9 illustrates an example of deriving a division structure of atarget block based on a plurality of reference blocks.

FIG. 10 illustrates an example of a sequence for coding a picture in arandom access form and an output sequence.

FIG. 11 illustrates various examples of block division structureintegration.

FIG. 12 illustrates an example of derivation of an integrated blockdivision structure.

FIG. 13 illustrates an example of a comparison between the data amountof the existing division information and the data amount of the divisioninformation according to the present invention.

FIG. 14 schematically illustrates an example of a video encoding methodaccording to the present invention.

FIG. 15 schematically illustrates an example of a video decoding methodaccording to the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention can be modified in various forms, and specificembodiments thereof will be described and shown in the drawings.However, the embodiments are not intended for limiting the invention.The terms used in the following description are used to merely describespecific embodiments, but are not intended to limit the invention. Anexpression of a singular number includes an expression of the pluralnumber, so long as it is clearly read differently. The terms such as“include” and “have” are intended to indicate that features, numbers,steps, operations, elements, components, or combinations thereof used inthe following description exist and it should be thus understood thatthe possibility of existence or addition of one or more differentfeatures, numbers, steps, operations, elements, components, orcombinations thereof is not excluded.

On the other hand, elements in the drawings described in the inventionare independently drawn for the purpose of convenience for explanationof different specific functions in an image encoding/decoding device anddoes not mean that the elements are embodied by independent hardware orindependent software. For example, two or more elements of the elementsmay be combined to form a single element, or one element may be dividedinto plural elements. The embodiments in which the elements are combinedand/or divided belong to the invention without departing from theconcept of the invention.

Hereinafter, exemplary embodiments of the invention will be described indetail with reference to the accompanying drawings.

FIG. 1 is a block diagram schematically illustrating a video encodingdevice according to an embodiment of the invention.

Referring to FIG. 1, a video encoding device 100 includes a picturepartitioner 105, a predictor 110, a transformer 115, a quantizer 120, arearranger 125, an entropy encoder 130, a dequantizer 135, an inversetransformer 140, a filter 145, and memory 150.

The picture partitioner 105 may be configured to split the input pictureinto at least one processing unit block. In this connection, a block asa processing unit may be a prediction unit PU, a transform unit TU, or acoding unit CU. The picture may be composed of a plurality of codingtree unit CTUs. Each CTU may be split into CUs as a quad tree structure.The CU may be split into CUs having a deeper depth as a quad-treestructures. The PU and TU may be obtained from the CU. For example, thePU may be partitioned from a CU into a symmetric or asymmetric squarestructure. Also, the TU may be split into a quad tree structure from theCU. CTU may correspond to CTB (coding tree block), CU may correspond toCB (coding block), PU may correspond to PB (prediction block), and TUmay correspond to TB (transform block).

The predictor 110 includes an inter prediction unit that performs aninter prediction process and an intra prediction unit that performs anintra prediction process, as will be described later. The predictor 110performs a prediction process on the processing units of a picturedivided by the picture dividing module 105 to create a prediction blockincluding a prediction samples or a prediction samples array. In thepredictor 110, the processing unit of a picture may be a CU, a TU, or aPU. The predictor 110 may determine whether the prediction performed onthe corresponding processing unit is an inter prediction or an intraprediction, and may determine specific details for example, a predictionmode of the prediction methods. The processing unit subjected to theprediction process may be different from the processing unit of whichthe prediction method and the specific details are determined. Forexample, the prediction method and the prediction mode may be determinedin the units of PU and the prediction process may be performed in theunits of TU.

In the inter prediction, a prediction process may be performed based oninformation on at least one of a previous picture and/or a subsequentpicture of a current picture to create a prediction block. In the intraprediction, a prediction process may be performed based on pixelinformation of a current picture to create a prediction block.

As an inter prediction method, a skip mode, a merge mode, and AdvancedMotion Vector Prediction (AMVP) may be used. In inter prediction, areference picture may be selected for the PU and a reference blockcorresponding to the PU may be selected. The reference block may beselected on an integer pixel (or sample) or fractional pixel (or sample)basis. Then, a prediction block is generated in which the residualsignal with respect to the PU is minimized and the motion vectormagnitude is also minimized. Pixels, pels and samples are usedinterchangeably each other herein.

A prediction block may be generated as an integer pixel unit, or as afractional pixel unit such as a ½ pixel unit or a ¼ pixel unit. In thisconnection, a motion vector may also be expressed as a fractional pixelunit.

Information such as the index of the reference picture selected via theinter prediction, the motion vector difference MVD, the motion vectorpredictor MVP, residual signal, etc., may be entropy encoded and thentransmitted to the decoding device. When the skip mode is applied, theprediction block may be used as a reconstruction block, so that theresidual may not be generated, transformed, quantized, or transmitted.

When the intra prediction is performed, the prediction mode may bedetermined in the unit of PU and the prediction process may be performedin the unit of PU. Alternatively, the prediction mode may be determinedin the unit of PU and the inter prediction may be performed in the unitof TU.

The prediction modes in the intra prediction may include 33 directionalprediction modes and at least two non-directional modes, as an example.The non-directional modes may include a DC prediction mode and a planarmode.

In the intra prediction, a prediction block may be constructed after afilter is applied to a reference sample. At this time, it may bedetermined whether a filter should be applied to a reference sampleaccording to the intra prediction mode and/or the size of a currentblock.

Residual values (a residual block or a residual signal) between theconstructed prediction block and the original block are input to thetransformer 115. The prediction mode information, the motion vectorinformation, and the like used for the prediction are encoded along withthe residual values by the entropy encoder 130 and are transmitted tothe decoding device.

The transformer 115 performs a transform process on the residual blockin the unit of TUs and generates transform coefficients.

A transform block is a rectangular block of samples and is a block towhich the same transform is applied. The transform block may be a TU andmay have a quad-tree structure.

The transformer 115 may perform a transform process according to theprediction mode applied to a residual block and the size of the block.

For example, when intra prediction is applied to a residual block andthe residual block has an 4×4 array, the residual block is transformedusing discrete sine transform DST. Otherwise, the residual block may betransformed using discrete cosine transform DCT.

The transformer 115 may construct a transform block of transformcoefficients through the transform.

The quantizer 120 may quantize the residual values, that is, transformcoefficients, transformed by the transformer 115 and may createquantization coefficients. The values calculated by the quantizer 120may be supplied to the dequantizer 135 and the rearranger 125.

The rearranger 125 may rearrange the transform coefficients suppliedfrom the quantizer 120. By rearranging the quantization coefficients, itis possible to enhance the encoding efficiency in the entropy encoder130.

The rearranger 125 may rearrange the quantized transform coefficients inthe form of a two-dimensional block to the form of a one-dimensionalvector through the use of a coefficient scanning method.

The entropy encoder 130 may be configured to entropy code the symbolaccording to a probability distribution based on the quantized transformvalues rearranged by the rearranger 125 or the encoding parameter valuecalculated during the encoding process, etc. and then to output abitstream. The entropy encoding method is a method of receiving a symbolhaving various values and expressing the symbol as a binary string thatcan be decoded while removing statistical redundancy thereof.

In this connection, the symbol means the to-be encoded/decoded syntaxelement, coding parameter, residual signal value and so on. The encodingparameter is required for encoding and decoding. The encoding parametermay contain information that can be inferred during encoding ordecoding, as well as information encoded in an encoding device andpassed to a decoding device like the syntax element. The encodingparameter is the information needed to encode or decode the image. Theencoding parameter may include statistics or values such as for example,the intra/inter prediction mode, movement/motion vector, referencepicture index, coding block pattern, residual signal presence orabsence, transform coefficient, quantized transform coefficient,quantization parameter, block size, block partitioning information, etc.Also, the residual signal may mean a difference between an originalsignal and a prediction signal. Also, the difference between theoriginal signal and the prediction signal may be transformed to definethe residual signal, or the difference between the original signal andthe prediction signal may be transformed and quantized to define theresidual signal. The residual signal can be called the residual block inthe block unit, and can be called the residual samples in the sampleunit.

When the entropy encoding is applied, the symbols may be expressed sothat a small number of bits are allocated to a symbol having a highprobability of occurrence, and a large number of bits are allocated to asymbol having a low probability of occurrence. This may reduce the sizeof the bit string for the to-be-encoded symbols. Accordingly, thecompression performance of image encoding may be increased via theentropy encoding.

Encoding schemes such as exponential Golomb, Context-Adaptive VariableLength Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding(CABAC) may be used for the entropy encoding. For example, the entropyencoder 130 may store therein a table for performing entropy encoding,such as a variable length coding/code (VLC) table. The entropy encoder130 may perform entropy encoding using the stored VLC table. Also, theentropy encoder 130 derives a binarization method of a correspondingsymbol and a probability model of a corresponding symbol/bin, and thenperforms entropy encoding using the derived binarization method orprobability model.

The entropy encoder 130 may give a predetermined change to a parameterset or syntaxes to be transmitted, when necessary.

The dequantizer 135 dequantizes the values transform coefficientsquantized by the quantizer 120. The inverse transformer 140 inverselytransforms the values dequantized by the dequantizer 135.

The residual value or residual samples or residual samples arraygenerated by the dequantizer 135 and the inverse-transformer 140, andthe prediction block predicted by the predictor 110 may be combined toform a reconstructed block including a reconstructed sample or areconstructed sample array.

In FIG. 1, a residual block and a prediction block are added to create areconstructed block by an adder. At this time, the adder may beconsidered as a particular unit reconstructed block creating unit thatgenerates a reconstructed block.

The filter 145 applies a deblocking filter, an ALF Adaptive Loop Filter,an SAO Sample Adaptive Offset to the reconstructed picture.

The deblocking filter removes a block distortion generated at theboundary between blocks in the reconstructed picture. The ALF performs afiltering process based on the result values of the comparison of theoriginal picture with the reconstructed picture of which the blocks arefiltered by the deblocking filter. The ALF may be applied only when highefficiency is necessary. The SAO reconstructs offset differences betweenthe residual blocks having the deblocking filter applied thereto and theoriginal picture and is applied in the form of a band offset, an edgeoffset, or the like.

The memory 150 may store the reconstructed block or picture calculatedby the filter 145. The reconstructed block or picture stored in thememory 150 may be supplied to the predictor 110 that performs the interprediction.

FIG. 2 is a block diagram schematically illustrating a video decodingdevice according to an embodiment of the invention. Referring to FIG. 2,a video decoding device 200 may include an entropy decoder 210, arearranger 215, a dequantizer 220, an inverse transformer 225, apredictor 230, a filter 235, and memory 240.

When a video bitstream is input from the video encoding device, theinput bitstream may be decoded based on the order in which videoinformation is processed by the video encoding device.

The entropy decoder 210 may entropy-decode the input bitstream accordingto a probability distribution to generate symbols in a quantizedcoefficient form. The entropy decoding method is a method of receiving asequence of binary numbers and generating each of the symbols using thesequence. The entropy decoding method is similar to the entropy encodingmethod described above.

For example, when a Variable Length Coding VLC (hereinafter referred toas ‘VLC’) such as CAVLC is used to perform entropy encoding in a videoencoding device, the entropy decoder 210 may perform decoding using thesame VLC table as the encoding device used in the encoding device. Also,when CABAC is used to perform entropy encoding in a video encodingdevice, the entropy decoder 210 may perform the entropy decoding usingCABAC.

More specifically, the CABAC entropy decoding method may includereceiving a bin corresponding to each syntax element in a bitstream,determining a context model using to-be-decoded syntax elementinformation, decoding information of a neighboring block and ato-be-decoded block, or information of a symbol/bin decoded in aprevious step, and predicting a probability of occurrence of a binaccording to the determined context model and thus performing arithmeticdecoding of the bin to generate a symbol corresponding to a value ofeach syntax element. In this connection, after determining the contextmodel, the CABAC entropy decoding method may further include a step ofupdating the context model using the information of the decodedsymbol/bin to determine a context model of the next symbol/bin.

Information for constructing a predicted block out of the informationdecoded by the entropy decoder 210 may be supplied to the predictor 230,and the residual values, that is, the quantized transform coefficients,entropy-decoded by the entropy decoder 210 may be input to therearranger 215.

The rearranger 215 may rearrange the bitstream information, that is, thequantized transform coefficients, entropy-decoded by the entropy decoder210 based on the rearrangement method in the video encoding device.

The rearranger 215 may reconstruct and rearrange the coefficientsexpressed in the form of a one-dimensional vector into coefficients inthe form of a two-dimensional block. The rearranger 215 may scan thecoefficients based on the prediction mode applied to the current blocktransform block and the size of the transform block and may create anarray of coefficients quantized transform coefficients in the form of atwo-dimensional block.

The dequantizer 220 may perform dequantization based on the quantizationparameters supplied from the video encoding device and the coefficientvalues of the rearranged block.

The inverse transformer 225 may perform the inverse DCT and/or inverseDST of the DCT and/or DST, which has been performed by the transformerof the video encoding device, on the quantization result from the videoencoding device.

The inverse transform may be performed based on a transfer unit or apartition unit of a picture determined by the video encoding device. Thetransformer of the video encoding device may selectively perform the DCTand/or DST according to plural information pieces such as the predictionmethod, the size of a current block, and the prediction direction, andthe inverse transformer 225 of the video decoding device may perform theinverse transform based on the transform information on the transformperformed by the transformer of the video encoding device.

The predictor 230 generates a prediction block including predictionsamples or prediction samples array based on the prediction blockgeneration-related information provided by the entropy decoder 210 andthe previously decoded block and/or picture information provided fromthe memory 240.

When the prediction mode for the current PU is the intra predictionmode, the predictor 230 may perform the intra prediction to generate aprediction block based on pixel information in the current picture.

When the prediction mode for the current PU is the inter predictionmode, the predictor 230 may be configured to perform inter prediction ona current PU based on information included in at least one picture of aprevious picture or a subsequent picture to the current picture. In thisconnection, information about the motion information necessary for interprediction of the current PU provided in the video encoding device, suchas motion vector and reference picture index may be deduced via checkingthe skip flag and merge flag received from the encoding device.

The predictor 230 may generate a prediction block such that the residualsignal relative to the current block is minimized and the motion vectorsize is minimized when inter prediction is performed on the currentpicture.

On the other hand, the motion information derivation method may bechanged according to the prediction mode of the current block. Theprediction mode applied to inter prediction may include an AdvancedMotion Vector Prediction (AMVP) mode, a merge mode, and the like.

For example, when a merge mode is applied, the encoding device and thedecoding device may generate a merge candidate list using the motionvector of the reconstructed spatial neighboring block and/or the motionvector corresponding to the Col block which is a temporally neighboringblock. In the merge mode, the motion vector of the candidate blockselected in the merge candidate list is used as the motion vector of thecurrent block. The encoding device may transmit a merge index indicatinga candidate block having an optimal motion vector selected from thecandidate blocks included in the merge candidate list to the decodingdevice. In this case, the decoding device may derive the motion vectorof the current block using the merge index.

In another example, when the AMVP (Advanced Motion Vector Prediction)mode is applied, the encoding device and decoding device generate amotion vector predictor candidate list using a motion vector of areconstructed spatial neighboring block and/or a motion vectorcorresponding to a Col block as a temporal neighboring block. That is,the motion vector of the reconstructed spatial neighboring block and/orthe motion vector corresponding to the Col block as a temporalneighboring block may be used as a motion vector candidate. The encodingdevice may transmit to the decoding device a prediction motion vectorindex indicating the optimal motion vector selected from among themotion vector candidates included in the motion vector predictorcandidate list. In this connection, the decoding device may select theprediction motion vector for the current block from the motion vectorcandidates included in the motion vector candidate list using the motionvector index.

The encoding device may obtain the motion vector difference MVD betweenthe motion vector for the current block and the motion vector predictor(MVP), encode the MVD, and transmit the encoded MVD to the decodingdevice. That is, the MVD may be a value obtained by subtracting themotion vector predictor (MVP) from the motion vector (MV) for thecurrent block. In this connection, the decoding device may decode thereceived motion vector difference, and derive the motion vector for thecurrent block via addition between the decoded motion vector differenceand the motion vector predictor.

Also, the encoding device may transmit a reference picture indexindicating a reference picture to the decoding device.

The predictor 230 of the decoding device may predict the motion vectorof the current block using the motion information of the neighboringblock and derive the motion vector of the current block using theresidual received from the encoding device. The decoding device maygenerate prediction sample (or prediction sample array) for the currentblock based on the derived motion vector and the reference picture indexinformation received from the encoding device.

The decoding device may generate a reconstructed sample (orreconstructed sample array) by adding a predictive sample (or apredictive sample array) and a residual sample (a residual sample array)obtained from the transform coefficients transmitted from the encodingdevice. And a reconstructed block and a reconstructed picture can begenerated based on thereon.

In the above-described AMVP and merge modes, motion information of thereconstructed neighboring block and/or motion information of the Colblock may be used to derive motion information of the current block.

In the skip mode, which is one of the other modes used for interprediction, neighboring block information may be used for the currentblock as it is. Accordingly, in the case of skip mode, the encoder doesnot transmit syntax information such as the residual to the decodingdevice in addition to information indicating which block's motioninformation to use as the motion information for the current block.

The reconstructed block may be generated using the predicted blockgenerated by the predictor 230 and the residual block provided by theinverse-transformer 225. FIG. 2 illustrates that using the adder, thepredicted block and the residual block are combined to generate thereconstructed block. In this connection, the adder may be viewed as aseparate element (a reconstructed block generator) that is configured togenerate the reconstructed block. In this connection, the reconstructedblock includes reconstructed samples or a reconstructed samples array asdescribed above; the predicted block includes a prediction samples or aprediction samples array; the residual block may include a residualsamples or a residual samples array. Accordingly, the reconstructedsamples or the reconstructed samples array can be considered to begenerated by combining the corresponding prediction samples orprediction samples array with the corresponding residual samples orresidual samples array.

When the skip mode is used for a block, the residual signal may not betransmitted and the predicted block may be used as a reconstructedblock.

The reconstructed block and/or picture may be supplied to the filter235. The filter 235 may perform a deblocking filtering operation, an SAOoperation, and/or an ALF operation on the reconstructed block and/orpicture.

The memory 240 may store the reconstructed picture or block for use as areference picture or a reference block and may supply the reconstructedpicture to an output unit.

The elements that is directly related to decoding images among theentropy decoder 210, the rearranger 215, the dequantizer 220, theinverse transformer 225, the predictor 230, the filter 235 and thememory 240 which are included in the decoding device 200, for example,the entropy decoder 210, the rearranger 215, the dequantizer 220, theinverse transformer 225, the predictor 230, the filter 235, and so onmay be expressed as a decoder or a decoding module that is distinguishedfrom other elements.

In addition, the decoding device 200 may further include a parser notshown in the drawing that parses information related to the encodedimages included in a bitstream. The parser may include the entropydecoder 210, and may be included in the entropy decoder 210. Such aparser may also be implemented as an element of the decoding module.

In order to efficiently compress the image, a block-unit divisionstructure is used. The picture may be divided into a plurality of unitblocks having the same size, and the unit blocks may be recursivelydivided and divided into blocks of the type most suitable for coding andcompression for each unit block. Here, the unit block may correspond toa coding tree unit (CTU), and a block further divided in the unit blockmay correspond to a coding unit. Here, the coding unit may mean a basicunit for processing an image in a process of the above-described imageprocessing, for example, intra/inter prediction, transform, quantizationand/or entropy coding.

FIG. 3 illustrates an example of a fixed block division structure and avariable block division structure.

Referring to FIG. 3, one picture may be divided into a fixed blockdivision structure as shown in FIG. 3(a) or a variable block divisionstructure as shown in FIG. 3(b). In the case of the fixed block divisionstructure, the side information for block division can be minimized. Inthe case of the variable block division structure, the side informationis relatively increased, but the coding unit of the optimal size may bedetermined in consideration of image characteristics.

FIG. 4 illustrates the concept of coding unit division.

The coding unit may have a rectangular shape, and one coding unit mayagain be divided into several coding units. For example, one coding unithaving a size of 2N×2N may be divided again into coding units havingfour N×N sizes. The division process of such a coding unit can be maderecursive, and not all the coding units need be divided into the sameform. However, there may be a limitation on the maximum size or theminimum size of the coding unit for convenience in encoding andprocessing. When the largest size of the coding unit is determined, itis referred to as the size of the largest coding unit (LCU), and whenthe smallest size of the coding unit is determined, it is referred to asthe size of the smallest coding unit (SCU). Here, the maximum codingunit may be referred to as a coding tree unit (CTU), the coding treeunit may be referred to as a coding tree block (CTB), and the codingunit may be referred to as a coding block (CB).

For one coding unit, information indicating whether or not the codingunit is divided may be specified. For example, if the value of the splitflag indicating whether to be divided 1, the corresponding coding unitis again divided into four coding units. If the value of the split flagis 0, the corresponding coding unit is not further divided, and theprocess for the corresponding coding unit can be performed, andprediction and conversion, etc., can be performed based on the codingunit.

The division structure of the coding unit described above can berepresented using a tree structure. For example, division may be madewith the maximum coding unit as the root. The coding unit in which thecurrent division is made becomes a parent node, and the coding unitdivided from the parent node becomes a child node. At this time, thecoding unit (parent node) in which the current division is made haschild nodes as many as the number of the divided coding units. And thecoding unit which is not further divided becomes a leaf node. A leafnode is a node that has no child nodes.

Assuming that a square division is made for one coding unit, one codingunit can be divided into a maximum of four sub-coding units, so that thedivision structure of the coding unit will be a quad tree structure.

In the encoding device, the maximum and minimum coding unit sizes aredetermined according to characteristics (e.g., resolution, etc.) of thevideo image or in consideration of efficiency of encoding, andinformation about the maximum and minimum coding unit sizes orinformation capable of drawing such information can be included in thebitstream. In addition, a coding unit having a tree structure can behierarchically divided with depth information. Each divided sub-codingunit may have depth information. The depth information indicates thenumber and/or degree of division of the coding unit, and therefore mayinclude information on the size of the sub-coding unit.

For example, assuming that the maximum coding unit size and the maximumdepth of the tree are defined and that the square division is performed,the coding unit size becomes a half the size of the parent node codingunit, and thus the minimum encoding unit size can be obtained by usingthe maximum coding unit size and maximum depth information. Conversely,the maximum coding unit size can be derived and utilized by predefiningthe minimum coding unit size and the maximum depth of the tree. Sincethe unit size in a square division can be obtained in the form of amultiple of 2, the size of the actual coding unit can be expressed as alogarithmic value of which the base is 2 so that the transmissionefficiency can be increased.

The decoding device can obtain the division information indicatingwhether the current coding unit is divided. Encoding/decoding efficiencycan be increased if such division information is acquired under aspecific condition, or if the encoding device is caused to transmit thedivision information under specific conditions. For example, if thecurrent coding unit is the minimum coding unit (SCU), it is no longerdivided into small coding units, so in this case it is not necessary toobtain the division information.

Referring to FIG. 4, the uppermost coding unit 410 may be referred to asa root node and has no parent node. Thus, the uppermost coding unit 410is a unit which is not divided from a higher coding unit than it is, andmay be a maximum coding unit (LCU). For example, the uppermost codingunit 410 may have the smallest depth value.

The uppermost coding unit 410 may be divided into a quadtree structureso that four sub-coding units 420 having a level 1 depth may begenerated. Here, at least one of the sub-coding units 420 having a level1 depth may be divided into a quadtree structure, or may not be furtherdivided. That is, the coding unit can be recursively divided into aquadtree structure until reaching the maximum depth (or maximum level)of the coding unit based on the uppermost coding unit 410.

For example, as shown in FIG. 4, if the maximum allowable depth of acoding unit is level 3, the uppermost coding unit 410 is divided into aquad tree structure recursively up to a depth of level 3, and sub-codingunits 420, 430, and 440 may be generated. Here, the sub-coding units420, 430, and 440 may be divided within the top-most coding unit (i.e.,one LCU) to have a division type such as reference numeral 450 of FIG.4.

FIG. 5 illustrates an example of coding unit division.

Referring to FIG. 5, a coding unit (CU) of depth 0 is not divided intosub-coding units when the split flag is 0, and is divided into foursub-coding units of depth 1 when the split flag is 1. Here, the foursubcoding units may be indexed from 0 to 3 in a raster scan order.

For example, based on no. 2 coding unit of depth 1, when the split flagof the coding unit 410 is 0, it is not divided into the sub-codingunits, and when the split flag is 1, it is recursively divided intosub-coding units of depth 2 as a quadtree structure. Until reaching themaximum depth (or last depth), the coding unit can be recursivelydivided into a quadtree structure.

According to such a CU quadtree division method, it is possible tominimize redundant side information by using a large-sized coding unitin a area where there are a small amount of movements and the texture issimple, while the residual signal can be minimized through more accurateprediction based on the coding unit of the small size in a area wherethere are a lot of movements and the texture is complicated.

Meanwhile, the block division according to the present invention notonly includes the block division of the square structure as describedabove, but also includes various rectangular divisions in addition tothe square division, or a combination of square and rectangulardivisions.

FIG. 6 illustrates an example of forward division and non-forwarddivision of a unit block.

Referring to FIG. 6, a unit block according to the present invention mayinclude a square division as in FIG. 6(a), and may include various typesof non-square divisions as shown in FIGS. 6(b) to 6(e).

As described above, the division information (ex. Split flag) for a unitblock is transmitted until a block (ex. CU) derived for division is nolonger divided.

FIG. 7 illustrates an example of information necessary for unit blockdivision.

Referring to FIG. 7, in the case of a unit block having the divisionstructure as shown in FIG. 7(a), it should be determined whetheradditional division is to be performed at each step as shown in FIGS.7(b) to 7(e). That is, 15 division information sets of from 1 to 15 in(b) to (e) are required in the case of the unit block. Here, 1 to 15indicate that there is information indicating whether or not the areaindicated by each number is further divided. The division informationcan be transmitted in a flag or index form for each block that can bedivided, and the amount of the division information also increases whenthe size of an image or a picture becomes large.

In the present invention, a method for reducing the amount of data usedto express the division structure of the target block by reusing blockdivision structure or information of the temporal neighboring picturewhich is temporally adjacent to the current picture or additionallyperforming extension based on the block division structure orinformation of the temporal neighboring picture is proposed. As aresult, video compression performance can be improved andencoding/decoding complexity can be reduced. Hereinafter, theneighboring picture may include temporally neighboring pictures.Further, the target block may include the above-described unit block (orCTU), or may include a block of any size.

FIG. 8 illustrates an example of a reference block of a neighboringpicture and a target block of a current picture corresponding thereto.

Referring to FIG. 8, part or all of the divided structure of the targetblock may be derived from a reference block of a neighboring picture. Inthis case, the division information of the target block can be obtainedbased on the division information used for the reference block of theneighboring picture, instead of being acquired through the transmittedinformation. In this case, the reference block may be a unit block at asame position or a specific position of the neighboring picture or ablock of a specific size with respect to the target block. The referenceblock may be referred to as a reference unit block in some cases. Thedivision information used in the reference block may be applied to thetarget block as it is or the division information refined based on thedivision information may be applied to the target block according tocertain criteria. In this case, for example, the division information upto the depth level n is used as it is, and the division information fromthe depth level n+1 may be separately signaled or defined according to aspecific criterion. Here, n may be any integer greater than 0 and lessthan the value of the maximum depth level. For example, n may be any oneof 1, 2, and 3.

On the other hand, the application unit for deriving the block structureof the current picture based on the block structure of the neighboringpicture may be as follows.

a. Whole picture

b. One or more unit blocks

c. Block of a certain size

Whether or not to apply the block division information of theneighboring picture to the current picture (or the current unit block orthe like) for each of the units is determined through separateinformation transmission, is determined by deriving in accordance with aspecific criterion, or is determined by the combination of these twomethods. Hereinafter, the description will be made based on the targetblock, and the target block according to the present invention mayinclude a whole picture, a unit block, or a block having a specificsize.

For example, the transmitted information may be flag information (e.g.,a block structure prediction flag) indicating whether to derive adivided structure of a target block based on a divided structure of areference block of a neighboring picture, or may be index informationindicating a specific picture or a specific reference block.

Also, for example, when determining whether or not to apply the divisioninformation of the reference block of the neighboring picture to thetarget block is derived according to the specific criterion, thespecific criterion may include the following.

a. The division structure variation between reference blocks inneighboring pictures

b. The motion vector magnitude and/or variation of the reference blockin one or more neighboring pictures

c. Combination of a and b

In the case of a, when division structure variation between referenceblocks existing respectively in two or more neighboring pictures codedbefore a current picture is coded is smaller than a predefinedreference, division information of the target block can be derived basedon the division information for at least one of the reference blocks.The reference block is a block at the same position or at a specificposition in the neighboring picture with respect to the current block,as described above.

For example, assuming that there are two neighboring pictures codedbefore the current picture is coded (a first neighboring picture and asecond neighboring picture), the reference blocks corresponding totarget block may respectively exist in the first neighboring picture andthe second neighboring picture. In this case, if a reference blockexisting in the first neighboring picture is referred to as a firstreference block and a reference block existing in the second neighboringpicture is referred to as a second reference block, the divisionstructure variation may be detected based on the first reference blockand the second reference block. For example, when the first referenceblock and the second reference block have the same or substantially thesame division structure, it may mean that the area in which the targetblock is located is not an area in which there is a moving object but isan area like a background. Accordingly, it is determined that the targetblock has similar image characteristics to the reference blocks, and ablock structure that is the same as or similar to the divided structurefor at least one of the reference blocks may be applied to the targetblock.

Here, the division structure variation may be determined based on thefollowing criteria. For example, the division structure variation may bedetermined based on the size of an area having a non-identical divisionstructure among all reference blocks. For example, when the area havinga division structure that is different from the second reference blockin the entire area of the first reference block is within apredetermined reference (for example, 10%), the division information ofthe target block can be derived based on at least one divisioninformation among the reference blocks. In another example, the divisionstructure variation may be determined based on the amount of information(e.g., the number of split flags or split indexes) used to display anarea that is not the same among all the reference blocks. For example, k(e.g., 20) split flags are used for the representation of the entiredivision structure in the first reference block, and when the number ofthe reference blocks used to express an area having a division structurethat is different from the second reference block among them is within apredefined criterion (e.g., k/1; 20/10), the division information of thetarget block can be derived based on at least one division informationamong the reference blocks.

In the case of b, if the size of a motion vector of a reference blockexisting in a neighboring picture coded before the current picture iscoded is smaller than a predefined criterion, or if the amount of motionvector variation between reference blocks respectively existing inneighboring pictures coded before the current picture is coded is lessthan a predefined criterion, division information of the target blockmay be derived based on the division information of at least one of thereference blocks.

Herein, when one reference block includes a plurality of blocks and aplurality of motion vectors for the plurality of blocks exists, arepresentative motion vector or a representative motion vector magnitudefor the one reference block may be derived and used. Herein, therepresentative motion vector and the representative motion vectormagnitude may indicate a motion vector and a magnitude of a specificposition in the reference block, or the representative motion vectormagnitude may be based on an average or a median value of absolutevalues of the plurality of motion vectors. For example, assuming thatone motion vector may be stored in units of m×m (where m is a power of2, e.g., m=2⁴=16) for coded pictures stored in the decoded picturebuffer (DPB), if the size of the reference block is m×m, one motionvector stored for the reference block may become the representativemotion vector. Or if the size of the reference block is 4m×4m, a motionvector corresponding to a specific area (for example, a left upper endarea) of the four motion vectors stored for the reference block may bethe representative motion vector. Or the mean or median value of theabsolute values of the 4 motion vectors may be the representative motionvector magnitude. In addition, if the first reference block exists inthe first neighboring picture and the second reference block exists inthe second neighboring picture, the motion vector variation can bedetected based on the first reference block and the second referenceblock. In this case, the representative motion vector for each referenceblock may be detected and compared as described above.

If the motion vector magnitude of the reference block is smaller than apredefined criterion or the motion vector variation of the firstreference block and the second reference block is smaller than apredefined criterion, this means that even if the picture is changed,there is a high possibility that it is a area that is hardly moved orchanged, that is, a area such as a background. Accordingly, it isdetermined that the target block has similar image characteristics tothe reference blocks, and a block structure that is the same as orsimilar to the division structure for at least one of the referenceblocks may be applied to the target block.

On the other hand, even if there is little or no change in the divisionstructure between the reference blocks, the motion vector difference maybe large. For example, even if the direction and absolute value of amotion vector are different between two reference blocks, a similar casemay occur in the block structure. Accordingly, in this case, bycombining the methods a and b as in the above-mentioned c, a blockstructure identical to or similar to the division structure for at leastone of the reference blocks may be applied to the target block only whenthe division structure change between the reference blocks is equal toor smaller than the first threshold value, and the size at least one ofthe reference blocks among the reference blocks is smaller than thesecond threshold value or the motion vector variation between thereference blocks is smaller than the second threshold. For example, ifthe size of a motion vector in at least one reference block is less than4 in a pel unit or the difference in motion vector magnitude (ormagnitude of motion vector difference) between reference blocks is lessthan 4 in a quarter pel unit, and the ratio of the area in which thedivision structure between the reference blocks is less than 10%, ablock structure that is the same as or similar to the division structurefor at least one of the reference blocks may be applied to the targetblock.

The numerical values used in the above examples are only examples, andthese numerical values may be used as fixed values for the whole image,or may be signaled by pictures, slices or unit blocks.

FIG. 9 illustrates an example of deriving a division structure of atarget block based on a plurality of reference blocks.

Referring to FIG. 9, (b) shows a target block, and (a) and (c) showreference blocks of neighboring pictures corresponding to the targetblock. In (a) and (c), the shaded portion represents a area where thedivided structure is different. That is, in (a) and (c), the remainingparts except for the shaded part have the same block division structure.Therefore, a portion having the same division structure in (a) and (c)can be used as the division structure of the target block.

On the other hand, the following method can be applied to the area ofthe target block corresponding to the area where the division structuresbetween the reference blocks do not coincide with each other.

a. Transmission of information to represent the division structure

b. Judgment based on predetermined criteria as to which division blockof the reference block is to be taken

c. Separate information transmission on which reference block toretrieve the division structure

In the case of a, at least one division information (split flag,division index, etc.) for indicating a division structure with respectto the area of the target block corresponding to the area where thedivision structure does not coincide between the reference blocks may betransmitted from the encoding device to the decoding device. In thiscase, the decoding device may perform the division based on the divisioninformation with respect to the area of the target block correspondingto the mismatch area.

In the case of b, the encoding device and the decoding device determinethe division structure according to a predetermined criterion withrespect to the area of the target block corresponding to the area wherethe division structure does not coincide between the reference blocks.The predetermined criterion may be determined based on one or acombination of, for example, a direction of a neighboring picture withrespect to a current picture, a quality of a neighboring picture, adegree of division of the corresponding area, a division structurecommonly appearing in a plurality of neighboring pictures, a distancebetween the neighboring picture and the current picture, etc.

FIG. 10 illustrates an example of a sequence and an output sequence forcoding a picture in a random access form. FIG. 10 shows an example inwhich the GOP (group of pictures) is 8.

Referring to FIG. 10, the coding order and the output order of picturesmay be different from each other. The output order may be based on apicture order count (POC). When considering the POC 3 picture as thecurrent picture, the division structure can be determined based on thecombination of at least one or more of the following criteria withrespect to the area of the target block corresponding to the area wherethe divided structure does not coincide between the reference blocks.

(1) When there are a plurality of neighboring pictures, a picture havinga POC value lower than the POC of the current picture has priority. Forexample, when the pictures of POC 1, 2, 4, and 8 are used as theneighboring pictures of the current picture POC 3, the neighboringpictures of POC 1 and 2 have priority over the pictures of POC 4 and 8.

(2) When there are a plurality of neighboring pictures, neighboringpictures having the same or nearest quality criterion as the currentpicture have priority. For example, the picture quality may bedetermined based on a temporal layer and/or a quantization parameter(QP). When a high QP is used, the picture quality is lowered, and the QPincreases as the temporal layer increases. Thus, in the example of FIG.10, the neighboring picture of POC #1 has priority.

(3) A neighboring picture having a low degree of division of acorresponding area has priority. In this case, the area indicates amismatched area between neighboring pictures. For example, if thecorresponding area of the POC 2 neighboring picture is not divided andthe neighboring pictures of the remaining neighboring pictures aredivided, the POC 2 neighboring picture has priority.

(3) When there are three or more neighboring pictures, a majority ofneighboring pictures have the same division structure for the area, andif a few neighboring pictures represent another division structure, thestructure used for the majority of neighboring pictures has priority.Herein, the area indicates a division structure mismatch area betweenneighboring pictures as described above. For example, if the POC 1, 2,and 4 neighboring pictures have the same division structure for thecorresponding area, and only the POC 8 neighboring picture has adifferent division structure, the division structure used for the POC 1,2, and 4 neighboring pictures is applied first.

(4) Among neighboring pictures, neighboring pictures located temporallyclosest to the current picture have priority. Here, the determination asto whether they are temporally closest to the current picture is madebased on POC. That is, POC 2 and 4 neighboring pictures relatively closeto the current picture of POC 3 have priority over POC 1 and 8neighboring pictures. For example, in the case of combining thecriterion of (1) and the criterion of (4), the POC 2 neighboring picturehas the highest priority in this example.

Meanwhile, in the case of c, indication information for indicating aspecific reference picture or a reference block for an area of thetarget block corresponding to an area where the division structure doesnot coincide between the reference blocks may be transmitted from theencoding device to the decoding device. In this case, based on thereceived indication information, the decoding device may determine thereference block which is to be used as the basis when deriving theadditional division structure of the area of the target blockcorresponding to the mismatch area based on the received indicationinformation. For example, in FIG. 9, when the indication informationindicates the reference block (a), the division structure of thereference block (a) can be used for a portion of the target blockcorresponding to the shade portion. That is, in this case, the divisionstructure of the target block is the same as the division structure ofthe reference block (a). For example, the indication information may bea reference picture index or a reference block index.

On the other hand, as shown in FIG. 10, it is possible to have variousqualities in units of pictures in the encoding/decoding process. Thefact that a particular picture is encoded/decoded with a higher qualitymay mean allowing more information amount in terms of side informationand residual signal.

For a specific block to be encoded, the cost function for finding theoptimal combination of the additional information and the residualsignal can be expressed by the following equation.Cost=D+λR  [Equation 1]

Herein, D represents a distortion which is the difference between theoriginal signal and the prediction signal, R represents the data rate ofthe additional information, and λ is a parameter for the trade-offbetween D and R. λ has a characteristic proportional to a quantizationparameter QP.

As the QP value is lowered to improve the quality of the picture, the λis also reduced accordingly, and consequently the cost function becomesless sensitive to the change in R. That is, since the influence of theincrease of the additional information amount on the overall costfunction is lowered, it is divided into a more detailed block structure,and the distortion is reduced by using more specific additionalinformation by the divided areas, thereby reducing the overall cost.

Therefore, according to the present invention, when the quality level ofthe current picture is different from that of the neighboring picture,the block division structure acquired based on the reference block canbe additionally extended. That is, according to the present invention, adivision structure for a target block can be derived by refining a blockdivision structure acquired based on a reference block.

In the example of FIG. 10, in most of the cases, the QP of a later codedpicture is equal to or higher than a previously coded picture, and thusthe later coded picture has a lower quality. As can be seen from theabove relationship of the cost function formula, as the coding proceedsin the coding order, there is a high possibility that the later pictureis a picture having a relatively lower quality than the previouspictures, and is likely to have a relatively less detailed dividedstructure. Therefore, when the division structure of the target block isderived based on the division structure of the reference block of theneighboring picture in consideration of these characteristics, thedivision structure of the reference block can be integrated in a lessgranular unit. That is, according to the present embodiment, a seconddivision structure (an integrated block division structure) is derivedby performing integration based on the first division structure of areference block, and the final division structure may be derived basedon the second division structure. In this case, for example, if thefinal depth according to the first division structure is n, the seconddivision structure may have a division structure up to a depth n or less(e.g., n−1 or n−2). The final division structure for the target blockmay be the same as the second division structure, or may be a divisionstructure which is derived by segmentation according to additionalinformation and/or specific criteria based on the second divisionstructure.

FIG. 11 shows various examples of block division structure integration.

Referring to FIG. 11, (a) to (e) show a division structure and anintegration relation of a part of a reference block. (a) through (e)division structures can be integrated into equivalent or less granularunits as shown by the arrows.

In the case of (a), the integration is performed by the depth level 2.In the case of (b), the integration is performed by the depth level 1.In the case of (c), the integration is performed by the depth level 1,and it is an example of integrating vertically divided rectangulardetailed block structures. In the case of (d), the integration isperformed by the depth level 1 and it is an example of integrating therectangular detailed block structure which is divided in the horizontaldirection. In the case of (e), the existing block division structure isused as it is.

When deriving the integrated block division structure, three factors,that is, whether or not the integrated block division structure isapplied, the integrated block division structure application unit, andthe integrated block division structure level, should be determined. Theabove three factors can be determined in the following manner.

First of all, the unit for applying the integrated block divisionstructure and whether or not it is applicable can be determined based onthe following.

a. It is applied to the whole picture. Information indicating whether itis applied on a picture-by-picture basis is transmitted.

b. Alternatively, It is applied by unit blocks. Information indicatingwhether to be applied is transmitted.

c. Alternatively, it is defined in advance in a fixed manner, or theapplication unit and/or the size may be defined in advance in aparameter transmission stage such as a stationary definition, a sequenceparameter set (SPS), a picture parameter set (PPS), an adaptationparameter set (APS) or a slice header, and information indicatingwhether or not it is applicable is transmitted.

d. Alternatively, it is applied by unit blocks. Herein, as describedabove, the comparison with the threshold value is performed based on atleast one of the division structure variation, the motion vector size,and the motion vector variation amount between the reference blockswithout applying the separate application indication information, inorder to determine whether to perform application.

In addition, the integrated block division structure level can bedetermined based on the following. Herein, the integrated block divisionstructure level indicates how much depth levels are integrated in thedivision structure.

a. The additional information is transmitted, and only the additionaldivision information is transmitted based on the reference blockstructure to determine the integrated block division structure level.

b. Alternatively, it is possible to apply a predefined fixed level inadvance for each integrated block division structure application unit,apply an integrated block division structure level defined in parametertransfer stages such as SPS, PPS, APS, or slice header, or sendinformation indicating integrated block division structure level.

c. Alternatively, an integrated block division structure is applied to aunit block, but information indicating a separate integrated blockdivision structure level is not transmitted. As described above, atleast one of the division structure variation, the motion vectormagnitude, and the motion vector variation is used as the basis, andwhen at least one of the division structure variation, the motion vectormagnitude, and the motion vector variation is included in one or morereference ranges defined beforehand, an integrated block divisionstructure level corresponding to the reference range is applied.

According to the method a, for example, it is possible to derive anintegrated block division structure that is less subdivided than thedivision structure of the reference block, compare the divisionstructure of the reference block with the integrated block divisionstructure, to thereby transmit division information based thereon.

FIG. 12 illustrates an example of derivation of an integrated blockdivision structure.

Referring to FIG. 12, (a) shows a reference block division structure,and (b) shows an integrated block division structure derived byreferring to the division structure of the reference block. Based on theabove (a), there may exist various integrated block division structurecandidates theoretically as shown in (c). In this case, the integratedblock division structure may be derived based on the above-describedcriteria and/or explicit indication information. In this embodiment, athird candidate of the integrated block division structure candidates of(c) is derived as an integrated block division structure for the targetblock.

In this case, the division structure of the target block can be derivedbased on the derived integrated block division structure. In this case,the reference block division structure and the integrated block divisionstructure are compared to try to divide only the area having adifference (i.e., the less segmented area), and the division structurehaving the smallest cost function can be selected as a divisionstructure for the target block. For example, the encoding device mayderive additional division information for the area of difference, andmay encode the additional division information and transmit theadditional division information to the decoding device. The decodingdevice may derive a division structure for the target block based on theintegrated block division structure and the additional divisioninformation.

FIG. 13 illustrates an example of a comparison between the data amountof the existing division information and the data amount of the divisioninformation according to the present invention. FIG. 13 shows an examplein which the integrated block division structure derived from FIG. 12 isused.

Referring to FIG. 13, (a) shows the data amount of the divisioninformation according to the existing method, and (b) shows the dataamount of the division information according to the present invention.According to (a), it is necessary to transmit a total of 9 segment flagsin order to represent the division structure of the target block. On theother hand, according to (b), it is possible to additionally determinewhether or not the division is performed only when the division is lesssegmented (or the same case) based on the integrated block divisionstructure. Therefore, when the level reaches the same level as the depthlevel of each detailed block of the reference block, the divisioninformation may not be transmitted to the detailed block. In this case,as shown in (b), a total of four division information (split flags) maybe transmitted to indicate the division structure of the target block.As described above, the detailed block can correspond to the CU.

FIG. 14 schematically shows an example of a video encoding methodaccording to the present invention. The method disclosed in FIG. 14 canbe performed by an encoding device.

Referring to FIG. 14, the encoding device derives at least one referenceblock for a current block of a current picture (S1400). The at least onereference block may be located in a temporally neighboring picture ofthe current picture. That is, when there are a plurality of referenceblocks, each reference block may be located in a different neighboringpicture.

The encoding device derives a division structure of the target blockbased on the division structure of the at least one reference block(S1410). The encoding device can derive an optimal division structurefor the target block based on the RD cost. The additional informationcan be reduced when the division structure of the at least one referenceblock is used. The encoding device may perform the division for thetarget block using the division structure of the at least one referenceblock when it is determined that the RD cost is lower when the divisionstructure of the at least one reference block is used.

In this case, the encoding device may derive the division structure ofthe target block based on the division structure of the at least onereference block only in a specific case.

For example, the at least one reference block may include a firstreference block and a second reference block, and if the variation ofthe block division structure between the first reference block and thesecond reference block is smaller than a first threshold, the divisioninformation of the target block may be derived based on the divisioninformation of the at least one reference block.

In addition, for example, the encoding device may derive arepresentative motion vector magnitude for the at least one referenceblock, and if the representative motion vector magnitude is smaller thana second threshold value, the division structure of the target block maybe derived based on the division structure of the at least one referenceblock.

For example, if the motion vector variation between the first referenceblock and the second reference block is less than a third thresholdvalue, the encoding device may derive the division structure of thetarget block based on the division structure of the at least onereference block.

For example, the encoding device can detect an area having the samedivision structure based on the division structure of the firstreference block and the division structure of the second referenceblock, and can derive the division structure of the target block basedon the division structure for the detected area.

In addition, the encoding device may select a specific reference blockamong a plurality of reference blocks, and use the divided structure ofthe selected specific reference block as a division structure of thetarget block. In this case, the specific reference block may be locatedin a specific reference picture selected from the plurality of referencepictures based on at least one of a picture order count (POC) value anda temporal layer value of each of the plurality of reference pictures.Alternatively, the specific reference block may be located in areference picture having a POC value that has the smallest differencefrom the POC value of the current picture among the plurality ofreference pictures. Alternatively, the specific reference block may be areference block having the lowest degree of division among the pluralityof reference blocks. The encoding device may encode indicationinformation for indicating the specific reference picture or thespecific reference block to thereby be outputted through the bitstream.

As another example, the encoding device may derive an integrated blockdivision structure based on the division structure of the at least onereference block, and derive the division structure of the target blockbased on the integrated block division structure. In this case, thefinal depth level of the integrated block division structure may be setto be lower than the final depth level of the division structure of theat least one reference block. In this case, the encoding device cangenerate the integrated block division structure application flag andoutput it through the bit stream. When the depth level of the portioncorresponding to the depth level of the corresponding area according tothe integrated block division structure is lower than the final depthlevel of the area according to the division structure of the at leastone reference block, a split flag indicating whether to additionallydivide the corresponding area of the target block may be generated andtransmitted to the decoding device through the bitstream.

The encoding device divides the target block into a plurality ofdetailed blocks based on the derived division structure (S1420). Here,the target block may include a unit block (or CTU, CTB) as describedabove, or may include a block of any size. The detail block may alsoinclude a CU (or CB). Or the detailed block may include a PU or a TU.

The encoding device encodes the plurality of detailed blocks and outputsencoding parameters (S1430). The encoding device may output the encodingparameters in the form of a bitstream. The bitstream may be transmittedto a decoding device via a network or a storage medium. In this case,the encoding device may transmit separate information for indicating aprediction mode for each of the plurality of detail blocks. For example,prediction mode information for the first detailed block and predictionmode information for the second detailed block may be individuallygenerated and transmitted through the bitstream.

On the other hand, the encoding device generates flag information (e.g.,a block structure prediction flag) indicating whether or not to derivethe division structure of the target block based on the divisionstructure of the reference block of the neighboring picture and outputsthe information through the bitstream. Alternatively, the encodingdevice may generate index information indicating whether a neighboringpicture/reference block is to be used and output the generated indexinformation through the bitstream.

FIG. 15 schematically shows an example of a video decoding methodaccording to the present invention. The method disclosed in FIG. 15 canbe performed by a decoding device.

Referring to FIG. 15, the decoding device derives at least one referenceblock for a current block of a current picture (S1500). The at least onereference block may be located in a temporally neighboring picture ofthe current picture. That is, when there are a plurality of referenceblocks, each reference block may be located in a different neighboringpicture.

The decoding device derives the division structure of the target blockbased on the division structure of the target block based on thedivision structure of the at least one reference block (S1510).

In this case, the decoding device can derive the division structure ofthe target block based on the division structure of the at least onereference block only in a specific case.

For example, the decoding device can obtain flag information (e.g., ablock structure prediction flag) indicating whether to derive a divisionstructure of a target block based on the division structure of thereference block of the neighboring picture through the receivedbitstream. In this case, when the value of the obtained block structureprediction flag is 1, the decoding device can derive the divisionstructure of the target block based on the division structure of the atleast one reference block.

In addition, for example, the at least one reference block may include afirst reference block and a second reference block, and the decodingdevice may derive the division structure of the target block based onthe division structure of the at least one reference block when thevariation of the block division structure between the first referenceblock and the second reference block is smaller than the first thresholdvalue.

In addition, for example, the decoding device derives a representativemotion vector magnitude for the at least one reference block, and whenthe representative motion vector magnitude is smaller than a secondthreshold value, the division structure of the target block may bederived.

In addition, for example, when the motion vector variation between thefirst reference block and the second reference block is less than thethird threshold, the decoding device may divide the division structureof the target block based on the division structure of the at least onereference block.

For example, the decoding device can detect an area having the samedivision structure based on the division structure of the firstreference block and the division structure of the second referenceblock, and can derive the division structure of the target block basedon the division structure for the detected area.

Also, the decoding device may select a specific reference block fromamong a plurality of reference blocks, and use the division structure ofthe selected specific reference block as a division structure of thetarget block. In this case, the specific reference block may be locatedin a specific reference picture selected from the plurality of referencepictures based on at least one of a picture order count (POC) value anda temporal layer value of each of the plurality of reference pictures.Alternatively, the specific reference block may be located in areference picture having a POC value that has the smallest differencefrom the POC value of the current picture among the plurality ofreference pictures. Alternatively, the specific reference block may be areference block having the lowest degree of division among the pluralityof reference blocks. Alternatively, the decoding device may receive, viaa bit stream, indication information for indicating a specific referencepicture or a specific reference block.

As another example, the decoding device may derive an integrated blockdivision structure based on the division structure of the at least onereference block, and derive the division structure of the target blockbased on the integrated block division structure. In this case, thefinal depth level of the integrated block division structure may be setto be lower than the final depth level of the division structure of theat least one reference block. The decoding device may obtain anintegrated block division structure application flag from the bitstream,and when the value of the obtained integrated block division structureapplication flag indicates 1, the decoding device may derive theintegrated block division structure based on the division structure ofthe at least one reference block and derive the division structure ofthe target block based on the integrated block division structure. Whenthe depth level of the portion corresponding to the depth level of thecorresponding area according to the integrated block division structureis lower than the final depth level of the area according to thedivision structure of the at least one reference block, the decodingdevice may obtain a split flag indicting whether to additionally dividethe corresponding area of the target block from the bitstream.

The decoding device divides the target block into a plurality ofdetailed blocks based on the derived division structure (S1520). Here,the target block may include a unit block (or CTU, CTB) as describedabove, or may include a block of any size. The detailed block may alsoinclude a CU (or CB). Or the detailed block may include a PU or a TU.

The decoding device decodes the plurality of detailed blocks to generatereconstructed samples (S1530). In this case, the decoding device cangenerate prediction samples by applying various prediction methods tothe plurality of detailed blocks, and generate reconstruction samplesbased on the prediction samples. For example, the inter prediction modemay be used as the prediction mode for the first detailed block amongthe detailed blocks, and the intra prediction mode may be used as theprediction mode for the second detailed block. Alternatively, the skipmode may be applied to the plurality of detailed blocks so that theprediction samples for the corresponding detailed blocks may be directlyderived as reconstructed samples.

According to the present invention, the division structure of the targetblock of the current picture can be derived based on the divisioninformation of the reference block of the neighboring picture. As aresult, the data amount for the additional information signaled fordividing the current block of the current picture can be reduced, andthe overall coding efficiency can be improved.

The above description is only illustrative of the technical idea of thepresent invention. Therefore, those skilled in the art may make variousmodifications and variations to the above description without departingfrom the essential characteristics of the present invention.Accordingly, the embodiments disclosed herein are intended to beillustrative, not limiting, of the present invention. The scope of thepresent invention is not limited by these embodiments. The scope ofprotection of the present invention should be construed according to thefollowing claims.

When the embodiments of the present invention are implemented insoftware, the above-described method may be implemented by modules(processes, functions, and so on) that perform the functions describedabove. Such modules may be stored in memory and executed by a processor.The memory may be internal or external to the processor, and the memorymay be coupled to the processor using various well known means. Theprocessor may comprise an application-specific integrated circuit(ASIC), other chipsets, a logic circuit and/or a data processing device.The memory may include a ROM (read-only memory), a RAM (random accessmemory), a flash memory, a memory card, a storage medium, and/or otherstorage device.

What is claimed is:
 1. A video decoding method performed by a decodingapparatus, the video decoding method comprising: deriving at least onereference block for a target block; deriving a division structure of thetarget block based on a division structure of the at least one referenceblock; dividing the target block into a plurality of blocks based on thederived division structure; and decoding the plurality of blocks togenerate reconstructed samples, wherein the at least one reference blockcomprises a first reference block and a second reference block, andwherein the division structure of the target block is derived based onthe division structure of the at least one reference block when avariation of a block division structure between the first referenceblock and the second reference block is smaller than a first thresholdvalue.
 2. The video decoding method of claim 1, wherein the at least onereference block is located in a temporally neighboring picture of thecurrent picture in which the target block is located.
 3. The videodecoding method of claim 1, further comprising: obtaining a blockstructure prediction flag from a bitstream, wherein the divisionstructure of the target block is derived based on the division structureof the at least one reference block when a value of the obtained blockstructure prediction flag is
 1. 4. The video decoding method of claim 1,further comprising: deriving a representative motion vector magnitudefor the at least one reference block, wherein the division structure ofthe target block is derived further based on the division structure ofthe at least one reference block when a magnitude of the representativemotion vector is smaller than a second threshold value.
 5. The videodecoding method of claim 1, wherein the division structure of the targetblock is derived further based on the division structure of the at leastone reference block when a motion vector variation between the firstreference block and the second reference block is less than a thirdthreshold value.
 6. The video decoding method of claim 1, furthercomprising: detecting an area having the same division structure basedon the division structure of the first reference block and the divisionstructure of the second reference block, wherein the at least onereference block includes the first reference block and the secondreference block, and wherein the division structure of the target blockis derived based on a division structure for the detected area.
 7. Thevideo decoding method of claim 1, further comprising: selecting aparticular reference block from among a plurality of reference blocks,wherein the at least one reference block comprises the plurality ofreference blocks, wherein the plurality of reference blocks arerespectively located in a plurality of reference pictures, and whereinthe division structure of the selected particular reference block isused as the division structure of the target block.
 8. The videodecoding method of claim 7, wherein the particular reference block islocated in a specific reference picture selected from the plurality ofreference pictures based on at least one of a picture order count (POC)value and a temporal layer value of each of the plurality of referencepictures.
 9. The video decoding method of claim 7, wherein theparticular reference block is located in a reference picture having aPOC value that has the smallest difference from the POC value of thecurrent picture among the plurality of reference pictures.
 10. The videodecoding method of claim 1, wherein the deriving of the divisionstructure of the target block comprises: deriving an integrated blockdivision structure based on the division structure of the at least onereference block; and deriving the division structure of the target blockbased on the integrated block division structure.
 11. The video decodingmethod of claim 10, wherein a final depth level of the integrated blockdivision structure is lower than a final depth level of the divisionstructure of the at least one reference block.
 12. The video decodingmethod of claim 10, further comprising: obtaining an integrated blockdivision structure application flag from a bitstream, wherein, when avalue of the obtained integrated block division structure applicationflag indicates 1, an integrated block division structure is derivedbased on the division structure of the at least one reference block, andthe division structure of the target block is derived based on theintegrated block division structure.
 13. The video decoding method ofclaim 11, further comprising: obtaining a split flag from the bitstream,wherein, when a depth level of a portion corresponding to a depth levelof a corresponding area according to the integrated block divisionstructure is lower than a final depth level of an area according to adivision structure of the at least one reference block, the split flagindicates whether to further divide the corresponding area of the targetblock.
 14. A video encoding method performed by an encoding device, thevideo encoding method comprising: deriving at least one reference blockfor a target block; deriving a division structure of the target blockbased on a division structure of the at least one reference block;dividing the target block into a plurality of blocks based on thederived divided structure; and encoding the plurality of blocks tothereby output an encoding parameter, wherein the at least one referenceblock comprises a first reference block and a second reference block,and wherein the division structure of the target block is derived basedon the division structure of the at least one reference block when avariation of a block division structure between the first referenceblock and the second reference block is smaller than a first thresholdvalue.
 15. The video encoding method of claim 14, further comprising:deriving a representative motion vector magnitude for the at least onereference block, wherein the division structure of the target block isderived further based on the division structure of the at least onereference block when a magnitude of the representative motion vector issmaller than a second threshold value.
 16. The video encoding method ofclaim 14, wherein the division structure of the target block is derivedfurther based on the division structure of the at least one referenceblock when a motion vector variation between the first reference blockand the second reference block is less than a third threshold value. 17.The video encoding method of claim 14, further comprising: detecting anarea having the same division structure based on the division structureof the first reference block and the division structure of the secondreference block, wherein the at least one reference block includes thefirst reference block and the second reference block, and wherein thedivision structure of the target block is derived based on a divisionstructure for the detected area.
 18. The video encoding method of claim14, further comprising: selecting a particular reference block fromamong a plurality of reference blocks, wherein the at least onereference block comprises the plurality of reference blocks, wherein theplurality of reference blocks are respectively located in a plurality ofreference pictures, and wherein the division structure of the selectedparticular reference block is used as the division structure of thetarget block.
 19. The video encoding method of claim 14, wherein thederiving of the division structure of the target block comprises:deriving an integrated block division structure based on the divisionstructure of the at least one reference block; and deriving the divisionstructure of the target block based on the integrated block divisionstructure.